Interpretive Summary: The objective of this study was to evaluate the ability of a clay product to sorb and mitigate the toxic effects of a fungal toxin in the Nile tilapia fish. Growth, immunity, and the intestinal bacterial community were evaluated after feeding tilapia diets with or without the fungal toxin and with or without the clay for 10 weeks. The fungal toxin significantly decreased weight gain and immunity regardless of whether the clay was to fed to the fish. Intestinal bacterial communities were not affected by the fungal toxin. These results demonstrated that the toxic effects on fish production were potentially not the result of the toxin effects on intestinal bacteria that support digestion. Also, the clay was not an effective treatment against the negative effects of the toxin. These results are of great interest to researchers and producers of farm-reared fish.

Technical Abstract:
The objective of this study was to evaluate the ability of NovaSil (NS) clay to sorb and mitigate the toxic effects of aflatoxin B1 (AFB1) in Nile tilapia (Oreochromis niloticus). Growth performance, specific innate immunological function, intestinal microbial community, and histology were evaluated after feeding tilapia diets with or without AFB1 and/or NS for 10 weeks. Aflatoxin B1 at concentrations of 1.5 and 3.0 ppm significantly (P < 0.05) decreased weight gain, feed efficiency, hepatosomatic index, and macrophage extracellular superoxide anion production in tilapia, regardless of NS addition to the diet. The overall results regarding the efficacy of NS were mixed; however, there was a trend (P=0.157) towards AFB1-toxicity prevention in regards to macrophage extracellular superoxide anion production. Additionally, when 0.5 and 1% NS were included in diets containing 1.5 ppm AFB1, total histopathological score was lowered; however, this protective effect was not evident when fish were exposed to 3.0 ppm AFB1. Denaturing gradient gel electrophoresis was performed to assess the effects of both AFB1 and NS on gut microbiota, but no significant differences were found among treatment groups.